The address of a variable to retrieve the value of pname for the program interface.

Description

glGetProgramInterfaceiv queries the property of the interface identifed
by programInterface in program, the property name of
which is given by pname.

program must be the name of an existing program object. programInterface
is the name of the interface within program to query and must be one of the following
values:

GL_UNIFORM

The query is targeted at the set of active uniforms within program.

GL_UNIFORM_BLOCK

The query is targeted at the set of active uniform blocks within program.

GL_ATOMIC_COUNTER_BUFFER

The query is targeted at the set of active atomic counter buffer binding points within program.

GL_PROGRAM_INPUT

The query is targeted at the set of active input variables used by the first shader stage of program.
If program contains multiple shader stages then input variables from any stage other than the first
will not be enumerated.

GL_PROGRAM_OUTPUT

The query is targeted at the set of active output variables produced by the last shader stage of program.
If program contains multiple shader stages then output variables from any stage other than the last
will not be enumerated.

The query is targeted at the set of active subroutine uniform variables used by the vertex, tessellation control, tessellation evaluation,
geometry, fragment and compute shader stages of program, respectively.

GL_TRANSFORM_FEEDBACK_VARYING

The query is targeted at the set of output variables from the last non-fragment stage of program that would be
captured if transform feedback were active.

GL_BUFFER_VARIABLE

The query is targeted at the set of active buffer variables used by program.

GL_SHADER_STORAGE_BLOCK

The query is targeted at the set of active shader storage blocks used by program.

GL_TRANSFORM_FEEDBACK_BUFFER

The query is targeted at the set of active buffer binding points to which output variables in the
GL_TRANSFORM_FEEDBACK_VARYING interface are written.

pname identifies the property of programInterface
to return in params.

If pname is GL_ACTIVE_RESOURCES, the value returned is the number of
resources in the active resource list for programInterface. If the list
of active resources for programInterface is empty, zero is returned.

If pname is GL_MAX_NAME_LENGTH, the value returned is the length of the
longest active name string for an active resource in programInterface.
This length includes an extra character for the null terminator. If the
list of active resources for programInterface is empty, zero is
returned. It is an error to specify GL_MAX_NAME_LENGTH when programInterface
is GL_ATOMIC_COUNTER_BUFFER, as active atomic counter buffer resources are
not assigned name strings.

If pname is GL_MAX_NUM_ACTIVE_VARIABLES, the value returned is the number
of active variables belonging to the interface block or atomic counter
buffer resource in programInterface with the most active variables. If
the list of active resources for programInterface is empty, zero is
returned. When pname is GL_MAX_NUM_ACTIVE_VARIABLES, programInterface
must be GL_UNIFORM_BLOCK, GL_ATOMIC_COUNTER_BUFFER, or GL_SHADER_STORAGE_BLOCK.

If pname is GL_MAX_NUM_COMPATIBLE_SUBROUTINES, the value returned is the
number of compatible subroutines belonging to the active subroutine
uniform in programInterface with the most compatible subroutines. If
the list of active resources for programInterface is empty, zero is
returned. When pname is GL_MAX_NUM_COMPATIBLE_SUBROUTINES,
programInterface must be one of GL_VERTEX_SUBROUTINE_UNIFORM,
GL_TESS_CONTROL_SUBROUTINE_UNIFORM, GL_TESS_EVALUATION_SUBROUTINE_UNIFORM,
GL_GEOMETRY_SUBROUTINE_UNIFORM, GL_FRAGMENT_SUBROUTINE_UNIFORM, or
GL_COMPUTE_SUBROUTINE_UNIFORM.

Errors

GL_INVALID_ENUM is generated if identifier
is not one of the accepted object types.

GL_INVALID_VALUE is generated if program
is not the name of an existing sync object.

GL_INVALID_VALUE is generated if bufSize is
zero.

GL_INVALID_OPERATION is generated if pname is GL_MAX_NAME_LENGTH and
programInterface is GL_ATOMIC_COUNTER_BUFFER or GL_TRANSFORM_FEEDBACK_BUFFER,
since active atomic counter and transform feedback buffer resources are not assigned name strings.

GL_INVALID_OPERATION error is generated if pname is
GL_MAX_NUM_ACTIVE_VARIABLES and programInterface is not GL_UNIFORM_BLOCK,
GL_SHADER_STORAGE_BLOCK, GL_ATOMIC_COUNTER_BUFFER, or
GL_TRANSFORM_FEEDBACK_BUFFER.

If not NULL, length and label should be addresses
to which the client has write access, otherwise undefined behavior, including process termination
may occur.